Investigation of Various Intramuscular Volumes Delivered to the Semimembranosus Muscle of Cavia porcellus

The goal of this study is to provide quantitative data on the ideal volume for intramuscular (IM) injections into the semimembranosus muscle of guinea pigs weighing between 320 to 410 grams. This evaluation comprised 2 experiments. The first was to assess dispersion leakage of intramuscularly injected iohexol, a radiocontrast agent commonly used in Computed Tomography (CT), based on analysis of in vivo imaging. The second used varying volumes of intramuscularly injected sodium chloride (0.9% NaCl) to assess pain and pathology associated with IM injection. Hartley guinea pigs were injected IM with varying volumes of either iohexol or sodium chloride (150, 300, 500, 1000 and 1500 μL). In the iohexol experiment, results suggest IM volumes of 150 and 300 μL remain within the target muscle. In the experiment using sodium chloride, pain and pathology did not increase as IM volume increased. The pathology noted was related to needle tract through the musculature rather than the volume size of the injectate. The results did not reveal a correlation between volume of IM 0.9% NaCl and pain levels. We conclude that volume size correlates more with precision and accuracy of delivery into the intended muscle tissue. Regarding tissue distribution, our findings also suggest that the optimal capacity for IM injection in the semimembranosus muscle should be less than 500 μL.

Characterization of Brain Inflammation, Apoptosis, Hypoxia, Blood-Brain Barrier Integrity and Metabolism in Venezuelan Equine Encephalitis Virus (VEEV TC-83) Exposed Mice by In Vivo Positron Emission Tomography Imaging

Traditional pathogenesis studies of alphaviruses involves monitoring survival, viremia, and pathogen dissemination via serial necropsies; however, molecular imaging shifts this paradigm and provides a dynamic assessment of pathogen infection. Positron emission tomography (PET) with PET tracers targeted to study neuroinflammation (N,N-diethyl-2-[4-phenyl]-5,7-dimethylpyrazolo[1,5-a]pyrimidine-3-acetamide, [¹⁸F]DPA-714), apoptosis (caspase-3 substrate, [¹⁸F]CP-18), hypoxia (fluormisonidazole, [¹⁸F]FMISO), blood–brain barrier (BBB) integrity ([¹⁸F]albumin), and metabolism (fluorodeoxyglucose, [¹⁸F]FDG) was performed on C3H/HeN mice infected intranasally with 7000 plaque-forming units (PFU) of Venezuelan equine encephalitis virus (VEEV) TC-83. The main findings are as follows: (1) whole-brain [¹⁸F]DPA-714 and [¹⁸F]CP-18 uptake increased three-fold demonstrating, neuroinflammation and apoptosis, respectively; (2) [¹⁸F]albumin uptake increased by 25% across the brain demonstrating an altered BBB; (3) [¹⁸F]FMISO uptake increased by 50% across the whole brain indicating hypoxic regions; (4) whole-brain [¹⁸F]FDG uptake was unaffected; (5) [¹⁸F]DPA-714 uptake in (a) cortex, thalamus, striatum, hypothalamus, and hippocampus increased through day seven and decreased by day 10 post exposure, (b) olfactory bulb increased at day three, peaked day seven, and decreased day 10, and (c) brain stem and cerebellum increased through day 10. In conclusion, intranasal exposure of C3H/HeN mice to VEEV TC-83 results in both time-dependent and regional increases in brain inflammation, apoptosis, and hypoxia, as well as modest decreases in BBB integrity; however, it has no effect on brain glucose metabolism.

[18F]DPA-714 PET Imaging Reveals Global Neuroinflammation in Zika Virus-Infected Mice

PURPOSE

The association of Zika virus (ZIKV) infection and development of neurological sequelae require a better understanding of the pathogenic mechanisms causing severe disease. The purpose of this study was to evaluate the ability and sensitivity of positron emission tomography (PET) imaging using [18F]DPA-714, a translocator protein (TSPO) 18 kDa radioligand, to detect and quantify neuroinflammation in ZIKV-infected mice.

PROCEDURES

We assessed ZIKV-induced pathogenesis in wild-type C57BL/6 mice administered an antibody to inhibit type I interferon (IFN) signaling. [18F]DPA-714 PET imaging was performed on days 3, 6, and 10 post-infection (PI), and tissues were subsequently processed for histological evaluation, quantification of microgliosis, and detection of viral RNA by in situ hybridization (ISH).

RESULTS

In susceptible ZIKV-infected mice, viral titers in the brain increased from days 3 to 10 PI. Over this span, these mice showed a two- to sixfold increase in global brain neuroinflammation using [18F]DPA-714 PET imaging despite limited, regional detection of viral RNA. No measurable increase in ionized calcium binding adaptor molecule 1 (Iba-1) expression was noted at day 3 PI; however, there was a modest increase at day 6 PI and an approximately significant fourfold increase in Iba-1 expression at day 10 PI in the susceptible ZIKV-infected group relative to controls.

CONCLUSIONS

The results of the current study demonstrate that global neuroinflammation plays a significant role in the progression of ZIKV infection and that [18F]DPA-714 PET imaging is a sensitive tool relative to histology for the detection of neuroinflammation. [18F]DPA-714 PET imaging may be useful in dynamically characterizing the pathology associated with neurotropic viruses and the evaluation of therapeutics being developed for treatment of infectious diseases.

Evaluation of Volume of Intramuscular Injection into the Caudal Thigh Muscles of Female and Male BALB/c Mice (Mus musculus)

This study presents recommendations for intramuscular injection into the caudal thigh muscle of mice according to analysis of in vivo imaging of intramuscularly injected iohexol, a radiocontrast agent commonly used in CT imaging. An experienced laboratory animal technician using a Hamilton syringe intramuscularly injected iohexol into isoflurane-anesthetized female and male BALB/c mice. Injected volumes (25, 50, 100, and 200 μL) underwent CT scanning at 9 time points over a 3-h period. The distribution of the injectate in the muscles of the rear leg was examined over time for each volume group. Results indicated that 25- and 50-μL volumes remain intramuscularly. At 100 μL, mild to moderate leakage into the extramuscular tissues occurred. At 200 μL, leakage into the extramuscular tissues was moderate to severe. Our results suggest volumes of 50 μL or less are recommended for the caudal thigh muscles of mice when intramuscular pharmacokinetics are needed; volumes greater than 50 μL display variable distribution into extramuscular tissues, thus potentially yielding different pharmacokinetic profiles.

Countering Zika Virus: The USAMRIID Response

The United States Army Medical Research Institute of Infectious Diseases (USAMRIID) possesses an array of expertise in diverse capabilities for the characterization of emerging infectious diseases from the pathogen itself to human or animal infection models. The recent Zika virus (ZIKV) outbreak was a challenge and an opportunity to put these capabilities to work as a cohesive unit to quickly respond to a rapidly developing threat. Next-generation sequencing was used to characterize virus stocks and to understand the introduction and spread of ZIKV in the United States. High Content Imaging was used to establish a High Content Screening process to evaluate antiviral therapies. Functional genomics was used to identify critical host factors for ZIKV infection. An animal model using the temporal blockade of IFN-I in immunocompetent laboratory mice was investigated in conjunction with Positron Emission Tomography to study ZIKV. Correlative light and electron microscopy was used to examine ZIKV interaction with host cells in culture and infected animals. A quantitative mass spectrometry approach was used to examine the protein and metabolite type or concentration changes that occur during ZIKV infection in blood, cells, and tissues. Multiplex fluorescence in situ hybridization was used to confirm ZIKV replication in mouse and NHP tissues. The integrated rapid response approach developed at USAMRIID presented in this review was successfully applied and provides a new template pathway to follow if a new biological threat emerges. This streamlined approach will increase the likelihood that novel medical countermeasures could be rapidly developed, evaluated, and translated into the clinic.

Intracellular conversion and in vivo dose response of favipiravir (T-705) in rodents infected with Ebola virus

During the 2013-2016 Ebola virus (EBOV) outbreak in West Africa, our team at USAMRIID evaluated the antiviral activity of a number of compounds, including favipiravir (T-705), in vitro and in mouse and nonhuman primate (NHP) models of Ebola virus disease. In this short communication, we present our findings for favipiravir in cell culture and in mice, while an accompanying paper presents the results of NHP studies. We confirmed previous reports that favipiravir has anti-EBOV activity in mice. Additionally, we found that the active form of favipiravir is generated in mice in tissues relevant for the pathogenesis of EBOV infection. Finally, we observed that protection can be achieved in mice down to 8 mg/kg/day, which is lower than the dosing regimens previously reported. An accompanying paper reports the results of treating nonhuman primates infected with EBOV or with Marburg virus with oral or intravenous favipiravir.

Efficacy of favipiravir (T-705) in nonhuman primates infected with Ebola virus or Marburg virus

Favipiravir is a broad-spectrum antiviral agent that has demonstrated efficacy against Ebola virus (EBOV) in rodents. However, there are no published reports of favipiravir efficacy for filovirus infection of nonhuman primates (NHPs). Here we evaluated the pharmacokinetic profile of favipiravir in NHPs, as well as in vivo efficacy against two filoviruses, EBOV and Marburg virus (MARV). While no survival benefit was observed in two studies employing once- or twice-daily oral dosing of favipiravir during EBOV infection of NHPs, an antiviral effect was observed in terms of extended time-to-death and reduced levels of viral RNA. However, oral dosing in biosafety level-4 (BSL-4) presents logistical and technical challenges, and repeated anesthesia events may potentially worsen survival outcome in animals. For the third study of treatment of MARV infection, we therefore made use of catheters, jackets, and tethers for intravenous (IV) dosing and blood collection, which minimized the requirement for repeated anesthesia events. When MARV infection was treated with IV favipiravir, five of six animals (83%) survived infection, while all untreated NHPs succumbed. An accompanying report presents the results of favipiravir treatment of EBOV infection in mice.

Applications of in vivo imaging in the evaluation of the pathophysiology of viral and bacterial infections and in development of countermeasures to BSL3/4 pathogens

While preclinical and clinical imaging have been applied to drug discovery/development and characterization of disease pathology, few examples exist where imaging has been used to evaluate infectious agents or countermeasures to biosafety level (BSL)3/4 threat agents. Viruses engineered with reporter constructs, i.e., enzymes and receptors, which are amenable to detection by positron emission tomography (PET), single photon emission tomography (SPECT), or magnetic resonance imaging (MRI) have been used to evaluate the biodistribution of viruses containing specific therapeutic or gene transfer payloads. Bioluminescence and nuclear approaches involving engineered reporters, direct labeling of bacteria with radiotracers, or tracking bacteria through their constitutively expressed thymidine kinase have been utilized to characterize viral and bacterial pathogens post-infection. Most PET, SPECT, CT, or MRI approaches have focused on evaluating host responses to the pathogens such as inflammation, brain neurochemistry, and structural changes and on assessing the biodistribution of radiolabeled drugs. Imaging has the potential when applied preclinically to the development of countermeasures against BSL3/4 threat agents to address the following: (1) presence, biodistribution, and time course of infection in the presence or absence of drug; (2) binding of the therapeutic to the target; and (3) expression of a pharmacologic effect either related to drug mechanism, efficacy, or safety. Preclinical imaging could potentially provide real-time dynamic tools to characterize the pathogen and animal model and for developing countermeasures under the U.S. FDA Animal Rule provision with high confidence of success and clinical benefit.

Molecular sieving and mass spectroscopy reveal enhanced collagen degradation in rabbit atheroma

BACKGROUND

Collagen degradation is the major mechanism of atherosclerotic plaque destabilization. It is unknown whether collagen breakdown is involved into formation of early atherosclerotic lesions.

METHODS

Current paper describes a novel collagen degradation assay based on a combination of molecular sieving and mass spectroscopy. The first step of the assay consists of the extraction of total collagen from tissue. This extract includes both intact collagen and its breakdown products. Molecular sieving is used to isolate low molecular weight collagen fragments. Since the low molecular weight fraction of the extract may contain some non-collagenous molecular species, the collagen-specific amino acid hydroxyproline is quantified using mass spectroscopy.

RESULTS

This assay was validated in various experimental systems with known/predictable level of collagen breakdown in vitro, ex vivo and in vivo. When applied to cholesterol-fed rabbit aorta, it revealed enhanced collagen degradation in rabbit atheromas compared to unaffected aortic regions.

CONCLUSION

A novel assay has been developed to demonstrate enhanced collagen degradation in rabbit atherosclerotic plaques. Accurate quantification of collagen breakdown products should provide a new relevant end point in the analysis of plaque development and stability.

The combined effect of inhibiting both ACAT and HMG-CoA reductase may directly induce atherosclerotic lesion regression

We hypothesized that coadministration of avasimibe and simvastatin would limit size, composition and extent of atherosclerotic lesions and potentially promote lesion regression, since bioavailable ACAT inhibitors decrease monocyte-macrophage enrichment and HMG-CoA reductase inhibitors limit smooth muscle cell migration and proliferation. Male New Zealand white rabbits were sequentially fed a 0.5% cholesterol, 3% peanut oil, 3% coconut oil diet for 9 weeks and a chow-fat diet for 6 weeks prior to drug administration. A time zero control group was necropsied prior to drug administration and the progression control was fed various diets but untreated. Avasimibe (10 mg/kg), simvastatin (2.5 mg/kg) or combination of avasimibe (10 mg/kg) with simvastatin (2.5 mg/kg) were administered in the chow-fat diet for 8 weeks. Plasma total cholesterol exposure was unchanged by avasimibe but was reduced 21% by both simvastatin alone and in combination with avasimibe. Combination of avasimibe and simvastatin decreased VLDL-cholesterol exposure by 56%. VLDL+IDL lipid composition was similar in the progression control and simvastatin-treated animals. Administration of avasimibe alone or in combination with simvastatin reduced the cholesteryl ester fraction and increased the triglyceride fraction to comparable extents. Relative to the progression control, avasimibe plus simvastatin markedly decreased thoracic aortic cholesteryl ester content and lesion coverage by 50% and aortic arch lesion size and macrophage area by 75 and 73%, respectively. With respect to lesion regression, avasimibe+simvastatin decreased aortic arch lesion size by 64% and monocyte-macrophage area by 73% when compared to time zero. Based on these data, we conclude that despite changes in plasma total and lipoprotein cholesterol exposure and lipoprotein composition comparable to monotherapy, inhibition of both ACAT and HMG-CoA reductase may not only directly blunt lesion progression but also promote regression of pre-established atherosclerotic lesions.

Matrix metalloproteinase inhibition attenuates left ventricular remodeling and dysfunction in a rat model of progressive heart failure

BACKGROUND

Matrix metalloproteinase (MMP) activation contributes to tissue remodeling in several disease states, and increased MMP activity has been observed in left ventricular (LV) failure. The present study tested the hypothesis that MMP inhibition would influence LV remodeling and function in developing LV failure.

METHODS AND RESULTS

LV size and function were measured in 5 groups of rats: (1) obese male spontaneously hypertensive heart failure rats (SHHF) at 9 months (n=10), (2) SHHF at 13 months (n=12), (3) SHHF rats treated with an MMP inhibitor during months 9 to 13 (PD166793 5 mg. kg(-1). d(-1) PO; n=14), (4) normotensive Wistar-Furth rats (WF) at 9 months (n=12), and (5) WF at 13 months (n=12). Plasma concentrations of the MMP inhibitor (116+/-11 micromol/L) reduced in vitro LV myocardial MMP-2 activity by approximately 100%. LV function and geometry were similar in WF rats at 9 and 13 months. LV peak +dP/dt was unchanged at 9 months in SHHF but by 13 months was reduced in the SHHF group compared with WF (3578+/-477 versus 5983+/-109 mm Hg/s, P</=0.05). LV volume measured at an equivalent ex vivo pressure (10 mm Hg) was increased in SHHF at 9 months compared with WF (443+/-12 versus 563+/-33 mL, P</=0.05) and increased further by 13 months (899+/-64 mL, P</=0.05). LV myocardial MMP-2 activity was increased by approximately 2-fold in SHHF at 9 and 13 months. With MMP inhibition, LV peak +dP/dt was similar to WF values and LV volume was reduced compared with untreated SHHF values (678+/-28 mL, P</=0.05).

CONCLUSIONS

MMP activity contributes to LV dilation and progression to LV dysfunction in a rodent HF model, and direct MMP inhibition can attenuate this process.

MMP/TIMP expression in spontaneously hypertensive heart failure rats: the effect of ACE- and MMP-inhibition

OBJECTIVE

Determine the effect of a matrix metalloproteinase inhibitor (MMPi) and angiotensin converting enzyme inhibitor (ACEi) on collagen, MMP, tissue inhibitors of MMPs (TIMPs) expression in the spontaneously hypertensive heart failure (SHHF) rat.

METHODS

Six groups were tested: normotensive 9- and 13-month-old Wistar-Furth (WF) rats, 9-month-old SHHFs (compensatory hypertrophy), 13-month-old SHHFs with HF, and 13-month-old SHHFs orally administered with either an MMPi (PD166793, 5 mgkg(-1)day(-1)) or ACEi (quinapril, 10 mgkg(-1)day(-1)) for 4 months. Collagen volume fraction was assessed histomorphometrically. Left ventricular (LV) mRNA [MMP-1,-2,-3,-7,-9,-11,-13,-14; TIMP-1,-2,-3,-4; and collagen alpha1(I) and alpha1(III)] and protein (MMP-2 and MMP-9 zymographic activity; Western blot analysis of MMP-13, and TIMP-1,-2,-4) levels could be quantified.

RESULTS

Collagen mRNA levels were elevated in SHHFs compared to age-matched controls, but collagen volume fraction was elevated only in 13-month-old SHHFs (approximately 2x). Only MMP-2 mRNA levels increased significantly with HF. However, MMP-2 and MMP-9 zymographic activity, and MMP-13 protein levels increased. TIMP-1 and TIMP-2 mRNA and protein levels increased, and TIMP-4 protein levels decreased in SHHFs vs. controls. Both drug treatments reduced LV dilation; preserved systolic function; and normalized MMP/TIMP expression. Both drug treatments also reduced collagen volume fraction, but only quinapril reduced collagen mRNA levels and LV hypertrophy.

CONCLUSIONS

The divergent effect of MMPi and ACEi on collagen mRNA levels and hypertrophy indicate that drug efficacy is mediated by different pathways in the SHHF rat.

The ACAT inhibitor avasimibe reduces macrophages and matrix metalloproteinase expression in atherosclerotic lesions of hypercholesterolemic rabbits

Given the significance of cholesteryl ester (CE) accumulation in macrophage foam cell formation, we hypothesized that inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT) would produce a histologically stable lesion by limiting macrophage enrichment and thereby a source of matrix metalloproteinases (MMPs). Male New Zealand White rabbits were sequentially fed a cholesterol/fat diet for 9 weeks, a fat-only diet for 6 weeks, and 25 mg/kg avasimibe for 7 to 8 weeks. Avasimibe had no effect on plasma total cholesterol exposure. Plasma avasimibe maximal concentration and 24-hour area-under-the-curve levels were 178 ng/mL and 2525 ng. h/mL, respectively, after 7 weeks of treatment with 25 mg/kg avasimibe. The median inhibitory concentration against human monocyte-macrophage ACAT was 12 ng/mL when determined in the absence of albumin, and aortic arch avasimibe levels were 25 ng/g of tissue wet weight. Avasimibe reduced thoracic aortic and iliac-femoral CE content by 39%, the extent of thoracic aortic lesions by 41%, aortic arch cross-sectional lesions area by 35%, and monocyte-macrophage area by 27%. The reduction in monocyte-macrophage area reflected a change in cell number and not cell size. In the iliac-femoral artery, avasimibe decreased monocyte-macrophage content by 77% and reduced the macrophage-to-lesion ratio from 0.16 to 0.05. Within the aortic arch, the catalytic activity of latent and active MMP-9 was reduced by 65% and 33%, respectively; latent and active MMP-1 and MMP-3 activity measured collectively was decreased by 52% and 60%, respectively, and MMP-2 was unchanged. Aortic arch MMP-9, tissue inhibitor of matrix metalloproteinase (TIMP)-1, and TIMP-2 mRNA levels were reduced 29% to 39%, and MMP-2 mRNA levels increased. We conclude that the bioavailable ACAT inhibitor avasimibe can directly limit macrophage accumulation, resulting in the histological appearance of mainly fibromuscular lesions, and can potentially stabilize preestablished atherosclerotic lesions by reducing MMP expression within the lesion.

Recombinant adenovirus vector mediated expression of lipoprotein (a) [Lp(a)] in rabbit plasma

Lipoprotein (a) [Lp(a)] is a heterodimer of apolipoprotein (a) [apo(a)] and apolipoprotein B-100 (apoB-100) of low density lipoprotein linked by a disulfide bond. Apo(a) and apoB-100 are synthesized by the liver and covalently associate or couple to form Lp(a) extracellularly. Elevated plasma Lp(a) is an independent risk factor for vascular injury disorders such as restenosis after balloon angioplasty and accelerated graft atherosclerosis following heart transplantation. Lp(a) is not expressed in laboratory animals making studies of its pathophysiology difficult. To overcome this problem, we explored the possibility of generating Lp(a) in rabbit plasma using replication-deficient adenovirus vector mediated gene delivery. Rabbits were chosen because of their large vessels and unlike mouse or rat, rabbit apoB-100 could interact with apo(a) to generate Lp(a). The recombinant (r) adenovirus vector construct used encoded a 200 kDa apo(a) [Ad-apo(a)]. Ad-apo(a) injection into the rabbit marginal vein caused the appearance of plasma rLp(a). Injection of a r adenovirus vector expressing the bacterial LacZ gene (Ad-LacZ) or PBS (vehicle) did not result in detectable plasma rLp(a). These are the first results to demonstrate plasma expression of rLp(a) in rabbits using adenovirus vector mediated gene transfer. Therefore, this system may be suitable for investigating Lp(a)'s role in the development of vascular injury diseases in a rabbit model.

HMG-CoA reductase and ACAT inhibitors act synergistically to lower plasma cholesterol and limit atherosclerotic lesion development in the cholesterol-fed rabbit

Given the beneficial effects of HMG-CoA reductase and ACAT inhibitors on hypercholesterolemia and atherosclerosis, we hypothesized that coadministration would improve the hypolipidemic response and not only limit lesion development but also alter the cellular composition of atherosclerotic lesions so as to induce a stable atherosclerotic lesion morphology. Plasma total cholesterol exposure was reduced 29 and 39% with atorvastatin (2.5 mg/kg) and CI-976 (5 mg/kg), respectively, and 60% upon coadministration due primarily to reductions in VLDL-cholesterol. Modest changes in liver cholesterol ester (CE) content were observed with atorvastatin or CI-976; however, a striking 48% reduction was noted upon coadministration. Liver HMG-CoA reductase mRNA levels were reduced 73% by cholesterol feeding and drug treatment did not prevent the reduction; however, atorvastatin alone and upon coadministration blunted the decrease in LDL receptor mRNA levels. The CE content of the iliac-femoral was unaffected by atorvastatin but was reduced 35% by CI-976 and 53% upon coadministration. Thoracic aortic CE content was reduced 38% by atorvastatin, 48% by CI-976 and 80% upon coadministration. Iliac-femoral lesion and macrophage area were reduced 48 and 67% by atorvastatin, respectively, and 68 and 81% by CI-976 but upon coadministration only an 85% reduction in macrophage area was noted. Aortic arch cross-sectional lesion and macrophage area were unaffected by atorvastatin, decreased 72-80% by CI-976 and reduced 87-92% upon coadministration. We conclude that inhibition of HMG-CoA reductase and ACAT acts synergistically to lower plasma total and lipoprotein cholesterol levels and to limit the development of atherosclerotic lesions in the cholesterol-fed rabbit by presumably regulating cholesterol trafficking pathways within liver and vascular cells.

alpha-Substituted malonester amides: tools to define the relationship between ACAT inhibition and adrenal toxicity

We prepared a series of alpha-substituted malonester amides that were evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyl transferase activity in vitro and to lower plasma total cholesterol levels in a variety of cholesterol-fed animal models. Compounds of this series were also useful in examining the relationship between adrenal toxicity and ACAT inhibition. One compound from this series, 9f, was a potent inhibitor of ACAT in both the microsomal and cellular assays. It was also bioavailable as determined by both a bioassay and a HPLC-UV assay. This compound was evaluated in both guinea pig and dog models of adrenal toxicity and compared to tetrazole amide 15. In the most sensitive species, the dog, both of these compounds achieved good plasma levels; however, compound 9f caused adrenal necrosis, whereas compound 15 had no effect on the adrenal gland. This adds to the growing body of evidence that the adrenal toxicity observed with ACAT inhibitors may not be mechanism related.

A specific 15-lipoxygenase inhibitor limits the progression and monocyte-macrophage enrichment of hypercholesterolemia-induced atherosclerosis in the rabbit

Oxidant signalling and lipoprotein oxidation may play important roles in atherosclerotic lesion development. Given coincident localization of 15-lipoxygenase (15-LO), stereospecific products of 15-LO and epitopes of modified LDL in atherosclerotic lesions, we hypothesized that inhibition of 15-LO by PD146176, an inhibitor of 15-LO with an IC50 in cells or isolated enzyme of 0.5-0.8 microM, may limit atherosclerotic lesion development through regulation of monocyte-macrophage enrichment. Rabbits exposed to chronic endothelial denudation of the iliac-femoral artery were meal-fed a 0.25% cholesterol (C), 3% peanut oil (PNO), 3% coconut oil (CNO) diet twice daily with and without 175 mg/kg PD146176 for 12 weeks. In a second study, atherosclerotic lesions were pre-established in rabbits through chronic endothelial denudation and meal-fed a 0.5% C, 3% PNO, 3% CNO diet for 9 weeks and a 0% C/fat diet for 6 weeks prior to an 8 week administration of PD146176 at 175 mg/kg, q.d. Plasma total and lipoprotein cholesterol exposure were similar in control and PD146176-treated animals in both studies but PD146176 increased plasma triglyceride exposure 2- to 4-fold. Plasma PD146176 concentrations ranged from 99 to 214 ng/ml at 2 h post-dose. In the progression study, the iliac-femoral monocyte-macrophage area was reduced 71%, cross-sectional lesion area was unchanged and cholesteryl ester (CE) content was reduced 63%. In the regression study, size and macrophage content of iliac-femoral, fibrous plaque-like lesions were decreased 34%, CE content was reduced 19% and gross extent of thoracic aortic lesions were reduced 41%. We conclude that PD146176 can limit monocyte macrophage enrichment of atherosclerotic lesions and can attenuate development of fibrofoamy and fibrous plaque lesions in the absence of changes in plasma total or lipoprotein cholesterol concentrations.

Animal models of atherosclerosis and interpretation of drug intervention studies

Atherosclerosis has often been defined as a multifactoral disease; however, a common risk factor associated with accelerated vascular disease in man or animals is an elevated plasma cholesterol level. Even though there is no one perfect animal model that completely replicates the stages of human atherosclerosis, cholesterol feeding and mechanical endothelial injury are two common features shared by most models of atherosclerosis. The models may differ with respect to degree of dietary cholesterol supplementation, length of hypercholesterolemia, dietary regimen and type, duration and degree of mechanical endothelial injury. With the advent of genetic engineering, transgenic mouse models have supplemented the classical dietary cholesterol induced disease models such as the cholesterol-fed hamster, rabbit, pig and monkey. The desire to limit the progression of atherosclerosis has spawned numerous drug intervention studies. Biochemical as well as morphologic and morphometric changes in the extent, structure and composition of atherosclerotic lesions following drug intervention have become major endpoints of in vivo drug intervention studies. Interpretations of alterations in vascular pathology following drug administration are often confounded by associated changes in plasma lipids and lipoproteins, limitation of the animal models and additional properties of compounds unrelated to their primary mode of action. Thus, the current review will summarize the pathology of atherosclerosis, describe various animal models of vascular disease and provide a critical review of the methods utilized and conclusions drawn when evaluating pharmacologic agents in animals.

Heterocyclic amides: inhibitors of acyl-CoA:cholesterol O-acyl transferase with hypocholesterolemic activity in several species and antiatherosclerotic activity in the rabbit

A series of heterocyclic amides were synthesized and evaluated as inhibitors of acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and for cholesterol lowering in cholesterol-fed rats. Compounds were evaluated for cell-based macrophage ACAT inhibition, bioactivity, and adrenal toxicity. Candidates were selected for evaluation in cholesterol-fed dogs and, ultimately, the injured cholesterol-fed rabbit model of atherosclerosis. The heterocyclic amides potently inhibited rabbit liver ACAT (IC50's = 0.014-0.11 microM), and the majority of compounds significantly lowered plasma cholesterol (42-68%) in an acute cholesterol-fed rat model at 3 mg/kg. The most efficacious compounds in the rat were evaluated for bioactivity in vivo and arterial ACAT inhibition in a cell-based macrophage ACAT assay. Two highly bioactive analogs, (+/-)-2-(3-dodecylisoxazol-5-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (13a) and (+/-)-2-(5-dodecylisoxazol-3-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (16a), were selected for further study and were found to be nontoxic in a guinea pig model of adrenal toxicity. Compounds 13a and 16a lowered total cholesterol in the cholesterol-fed rat, rabbit, and dog models of pre-established hypercholesterolemia. Compound 13a in the injured cholesterol-fed rabbit model of atherosclerosis was effective in slowing the development of cholesteryl ester-rich thoracic aortic lesions, reducing lesion coverage by 53% at a dose of 1 mg/kg.

Antiatherosclerotic activity of inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase in cholesterol-fed rabbits: a biochemical and morphological evaluation

Atherosclerotic lesion development was assessed in the thoracic aorta and chronically denuded iliac-femoral artery of hypercholesterolemic New Zealand White rabbits using inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase which have previously been shown to possess varying degrees of hepatoselectivity in rats. Atorvastatin, previously known as CI-981 (2.5 mg/kg), PD135022 (1.0 mg/kg), simvastatin (2.5 mg/kg), lovastatin (2.5 mg/kg), PD134965 (1.0 mg/kg), pravastatin (2.5 mg/kg) and BMY22089 (2.5 mg/kg) were added to a 0.5% cholesterol, 3% peanut, 3% coconut oil diet and fed for 8 weeks. Although reductions in plasma total cholesterol of 27% to 60%, VLDL-cholesterol of 31% to 71% and plasma total cholesterol exposure of 37% to 43% were obtained, no correlation between these parameters and vascular lipid content, lesion size or monocyte-macrophage content was noted. Iliac-femoral lipid content was unchanged; however, atorvastatin and simvastatin significantly reduced the cholesterol content of the thoracic aorta by 45%-62%. Atorvastatin and PD135022 reduced the size of the iliac-femoral lesion by 67% and monocyte-macrophage content by 72%. Simvastatin, lovastatin and PD134965 decreased the monocyte-macrophage content; however, lesion size was unchanged. Pravastatin and BMY22089 had no effect on lesion size or content. No compound significantly reduced the extent of thoracic aortic lesions. We concluded that changes in plasma lipids and lipoproteins noted with the various HMG-CoA reductase inhibitors did not account for the beneficial effect on atherosclerotic lesion development. The antiatherosclerotic potential of the HMG-CoA reductase inhibitors was compound-specific and clearly not a class effect.

Toxicologic effects of a novel acyl-CoA:cholesterol acyltransferase inhibitor in cynomolgus monkeys

PD 132301-2, an acyl-CoA: cholesterol acyltransferase (ACAT) inhibitor, was administered orally to cynomolgus monkeys for 2 wk at doses of 25, 50, 100, and 200 mg/kg to assess potential subacute toxicity. Sporadic episodes of soft feces and diarrhea increased in incidence from 100 to 200 mg/kg. Histopathologic alterations in adrenocortical cells of treated monkeys consisted of a dose-related decrease in cytoplasmic fine vacuolation and an increase in cytoplasmic eosinophilia most conspicuous in the zona fasciculata and reticularis. At 50, 100, and 200 mg/kg, a narrow discontinuous zone of cytotoxic cortical cell degeneration occurred in the outer zona fasciculata. Decreased fine vacuolation of cortical cells correlated ultrastructurally with reduced size and number of intracellular lipid vacuoles and biochemically with a dose-related decrease in adrenal total cholesterol (from 56 to 13% of control) and cholesteryl ester (from 51 to 3% of control) concentrations. Other ultrastructural changes noted in zona fasciculata cortical cells at all doses were an apparent increase in both smooth endoplasmic reticulum and variably sized autophagic vacuoles. Ovarian corpora lutea in some females at all doses had increased coarse vacuolation of luteal cells, foci of cellular degeneration, increased numbers of cholesterol clefts, and slight infiltrates of mononuclear cells. Sebaceous glands were atrophic in all treated monkeys due largely to a reduction in size and number of differentiated foam cells. Sebaceous gland reserve cells were hypertrophic and hyperplastic. Toxicity data from this study indicated that PD 132301-2 at 25-200 mg/kg targeted cholesterol-rich cells of the adrenals, ovaries, and skin adnexa.

Atherosclerotic lesion development in hypercholesterolemic Japanese quail following probucol treatment: a biochemical and morphologic evaluation

Probucol, a cholesterol-lowering agent which possesses antioxidant properties, was evaluated in hypercholesterolemic Japanese quail in order to assess the significance of antioxidant therapy on the development of atherosclerosis. Forty quail were fed a 0.5% cholesterol diet containing 0, 100, 200 or 500 mg kg-1 probucol for 2 months. At necropsy, plasma total and lipoprotein cholesterol and lipoprotein distribution were unchanged despite plasma probucol levels of 50 to 59 micrograms ml-1. The cholesteryl ester content of the liver and blood vasculature (brachiocephalic artery and aortic arch combined) was reduced by 33% and 62%, respectively, in animals given 500 mg kg-1 probucol. The vascular free cholesterol content was also reduced by 43 to 60% over the probucol dose range. Morphometric analysis of the brachiocephalic artery revealed that probucol reduced the incidence of lesions containing esterase-positive cells from 62% in untreated animals to 26% and 13% in animals administered 200 and 500 mg kg-1 probucol, respectively. No difference in mean wall thickness or area of the bracheocephalic artery was noted between the groups. Thus, we conclude that probucol can blunt the cholesteryl ester and macrophage enrichment of atherosclerotic lesions and this activity appears to be mediated by the compound's antioxidant properties since the changes noted were seen in the absence of alterations in plasma total and lipoprotein cholesterol levels.

The relationship between the degree of dietary-induced hypercholesterolemia in the rabbit and atherosclerotic lesion formation

A biochemical, histologic and morphometric evaluation of spontaneous, diet-induced (thoracic aorta) and injury-induced (iliac-femoral) atherosclerotic lesions was performed in rabbits maintained on varying levels of dietary cholesterol. Rabbits were meal-fed a 3% peanut oil, 3% coconut oil diet containing 0%, 0.1%, 0.25%, 0.5%, 1.0%, 1.5% or 2.0% cholesterol for 9 weeks. Plasma total cholesterol exposure (area under cholesterol-time curve (TC-AUC)) increased diet-dependently over the course of the study. VLDL and LDL cholesterol (VLDL-C, LDL-C) comprised 41% and 55%, respectively, of the plasma total cholesterol at cholesterol levels > 700 mg/dl (TC-AUC > 31,868 mg day/dl) and both VLDL-C and LDL-C were linearly related to TC-AUC (r = 0.98). Plasma TC-AUC was linearly related to thoracic aortic cholesteryl ester (CE) content (r = 0.74) and thoracic aortic lesion coverage (r = 0.66). In the injury-induced iliac-femoral lesion, plasma TC-AUC was linearly related to both iliac-femoral CE content (r = 0.80) and macrophage/lesion ratio (r = 0.64). At plasma cholesterol levels greater than 700 mg/dl, CE content of the iliac-femoral lesion ranged from 35 to 69 micrograms/mg dry defatted tissue, > 75% of the lesions were fibrofoamy in nature and macrophage/lesion area ratio was 0.46 to 0.55 while lesion area remained constant. VLDL-C and LDL-C were highly correlated with the CE content of both thoracic and iliac-femoral lesions, thoracic aortic lesion coverage and macrophage/lesion area ratio (r = 0.86-0.99). We conclude that the composition, extent and type of atherosclerotic lesion induced in rabbits is dependent upon the overall plasma cholesterol exposure, VLDL and LDL cholesterol content and whether lesions are induced by diet alone or both diet and chronic endothelial injury. In addition, various stages of atherosclerotic lesion formation can be replicated in the rabbit by titrating the animal's overall plasma cholesterol exposure.

Inhibition of acyl-CoA cholesterol O-acyltransferase reduces the cholesteryl ester enrichment of atherosclerotic lesions in the Yucatan micropig

Atherosclerotic lesion development may be altered indirectly by regulating plasma cholesterol or directly by inhibition of acyl-CoA cholesterol O-acyltransferase (ACAT) within cells of the artery. Yucatan micropigs were meal-fed a 2% cholesterol, 8% peanut oil, 8% coconut oil purified diet for 1 month prior to administration of the potent, bioavailable ACAT inhibitor CI-976, and induction of atherosclerotic lesions by chronic endothelial damage. After 84-108 days of therapy, CI-976 decreased mean plasma VLDL-cholesterol 85-91% and cumulative VLDL-exposure (area under VLDL-time curve) by 65%. However, overall plasma total, LDL and HDL cholesterol and triglyceride levels were unchanged. CI-976 decreased liver cholesteryl ester (CE) content 65% without significantly affecting adrenal CE content. The CE content of the injured left femoral, left iliac and abdominal aorta and uninjured right femoral and iliac arteries and thoracic aorta was reduced 62-78% by CI-976. Systemic plasma CI-976 levels measured 24 h post-dose ranged from 2.26 to 4.05 micrograms/ml and significantly correlated with the reduction in both VLDL and vessel CE content. Thus, we conclude that inhibition of ACAT can blunt the cholesteryl ester enrichment of developing atherosclerotic lesions by preventing reesterification and storage of lipoprotein cholesterol within vascular cells and by reducing the plasma level and delivery to the arterial wall of such atherogenic lipoproteins as VLDL.

Subacute toxicity of a novel inhibitor of acyl-CoA: cholesterol acyltransferase in beagle dogs

PD 132301-2 is a substituted urea hypolipidemic and antiatherosclerotic agent that is a potent inhibitor of acyl-CoA:cholesterol acyltransferase (ACAT). To determine its subacute toxicity, PD 132301-2 was administered orally to beagle dogs at 0, 6, 12, 25, 50, 200, 400, or 800 mg/kg/day for 2 weeks. Clinico-pathologic evaluations were completed on all dogs. Liver and adrenal total and esterified cholesterol concentrations, adrenocorticotrophic hormone (ACTH) responsiveness, and adrenal ultrastructure were determined at 0, 6, 12, and 25 mg/kg. At 12 mg/kg or greater, salivation, epiphora, conjunctivitis, emesis, anorexia or decreased food consumption, and soft to mucoid feces and/or diarrhea were noted. Suppression of ACTH response occurred by Day 6 at all doses. Adrenocortical degeneration and/or necrosis in zona fasciculata and reticularis was seen at all doses; adrenal free and esterified cholesterol were normal at 6 mg/kg and decreased at 12 and 25 mg/kg. Increases in serum alanine aminotransferase (2- to 15-fold), aspartate aminotransferase (2- to 12-fold), and alkaline phosphatase (2- to 7-fold) were noted at 50 mg/kg or greater. Periportal hepatocellular hypertrophy and hypereosinophilia occurred at 50 mg/kg or greater; hepatic cholesterol values were not significantly affected by treatment. Dose-dependent ultrastructural alterations in adrenocortical cells included decreased numbers of mitochondria and smooth endoplasmic reticulum profiles, qualitative and quantitative changes in lipid globules, and increased numbers of autolysosomes. PD 132301-2 or one of its metabolites has potent adrenocorticolytic properties and limited hepatotoxic properties by mechanism(s) that are likely independent of systemic ACAT inhibition.

Antiatherosclerotic effects of antioxidants are lesion-specific when evaluated in hypercholesterolemic New Zealand white rabbits

Oxidative modification of LDL may represent an initiating event in the formation of monocyte-macrophage foam cells, a major cell present in fatty streaks and atherosclerotic fibrous plaques. Therefore, we studied the effect of such antioxidants as probucol (500 mg/kg) and vitamins E and C (500 mg/kg each) on the regression of induced iliac-femoral lesions and progression of naturally occurring thoracic aortic fatty streak lesions in hypercholesterolemic New Zealand White rabbits. Following an initial 9-week lesion induction phase, both therapies were evaluated for 8 weeks. Probucol lowered plasma cholesterol 47% while vitamins E and C had no effect on plasma cholesterol. Probucol decreased the cholesteryl ester (CE) content of the thoracic aorta by 31% without changing the thoracic aortic lesion coverage. Vitamins E and C decreased thoracic aortic CE content by 40% and lesion coverage by 46%. Neither probucol nor vitamins E and C altered the CE content, lesion size, or macrophage/lesion ratio of the iliac-femoral artery. Thus, we conclude that the effects of antioxidants are specific to the stage of atherosclerotic lesion development. Antioxidant therapy alters the progression and cholesteryl ester enrichment of diet-induced thoracic aortic fatty streaks but has no effect on the progression and/or regression of more complicated injury-induced iliac-femoral lesions.

Hepatic and nonhepatic sterol synthesis and tissue distribution following administration of a liver selective HMG-CoA reductase inhibitor, CI-981: comparison with selected HMG-CoA reductase inhibitors

Since cholesterol biosynthesis is an integral part of cellular metabolism, several HMG-CoA reductase inhibitors were systematically analyzed in in vitro, ex vivo and in vivo sterol synthesis assays using [14C]acetate incorporation into digitonin precipitable sterols as a marker of cholesterol synthesis. Tissue distribution of radiolabeled CI-981 and lovastatin was also performed. In vitro, CI-981 and PD134967-15 were equipotent in liver, spleen, testis and adrenal, lovastatin was more potent in extrahepatic tissues than liver and BMY21950, pravastatin and PD135023-15 were more potent in liver than peripheral tissues. In ex vivo assays, all inhibitors except lovastatin preferentially inhibited liver sterol synthesis; however, pravastatin and BMY22089 were strikingly less potent in the liver. CI-981 inhibited sterol synthesis in vivo in the liver, spleen and adrenal while not affecting the testis, kidney, muscle and brain. Lovastatin inhibited sterol synthesis to a greater extent than CI-981 in the spleen, adrenal and kidney while pravastatin and BMY22089 primarily affected liver and kidney. The tissue distribution of radiolabeled CI-981 and lovastatin support the changes observed in tissue sterol synthesis. Thus, we conclude that a spectrum of liver selective HMG-CoA reductase inhibitors exist and that categorizing agents as liver selective is highly dependent upon method of analysis.

Comparison of CI-976, an ACAT inhibitor, and selected lipid-lowering agents for antiatherosclerotic activity in iliac-femoral and thoracic aortic lesions. A biochemical, morphological, and morphometric evaluation

Due to the potential importance of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) in the generation of lipid-filled monocytes-macrophages, the ACAT inhibitor CI-976 (2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide) was evaluated relative to selected lipid-lowering agents for their effect on atherosclerotic lesion regression and progression. Atherosclerotic lesions comparable in composition to human fatty streaks were induced by chronic endothelial denudation in the iliac-femoral artery of hypercholesterolemic New Zealand White rabbits before intervention, while naturally occurring fatty streaks developed in the thoracic aorta. CI-976 administered in a hypercholesterolemic diet at a dose that did not lower plasma cholesterol prevented the accumulation of monocytes-macrophages within the preestablished iliac-femoral lesion and reduced the foam cell area by 27-29% relative to the initiation of intervention. CI-976 also blunted the development of thoracic aortic fatty streak-like lesions and decreased the cholesteryl ester enrichment by 46%. CI-976 had no effect on plasma triglycerides and, more importantly, had no effect or decreased liver, iliac-femoral, and thoracic aortic free cholesterol content. Dietary intervention alone increased monocyte-macrophage involvement in the iliac-femoral lesion despite reductions in plasma, liver, and thoracic aortic cholesterol content. Conventional lipid-lowering therapy such as cholestyramine or cholestyramine/niacin required substantial decreases in plasma cholesterol levels to achieve comparable vascular changes. We conclude that inhibition of ACAT within the arterial wall by the potent and specific ACAT inhibitor CI-976, even in the absence of plasma cholesterol lowering, can result in the inhibition of atherosclerotic lesion progression and can enhance regression.

Dietary and mechanically induced rabbit iliac-femoral atherosclerotic lesions: a chemical and morphologic evaluation

The effect of combining chronic endothelial injury and intermittent meal feeding of a high and low cholesterol, coconut oil, peanut oil diet on plama lipid and lipoprotein content and on the formation of atherosclerotic lesions within the iliac-femoral artery of rabbits was studied. Alternate feeding of a 1 or 0.1% cholesterol, 3% coconut oil, 3% peanut oil diet for 3 to 14 weeks resulted in a 4- to 11-fold increase in plasma cholesterol with 59 to 79% of the plasma cholesterol eluting in a molecular weight fraction comparable to human low density lipoproteins (LDL). In the iliac-femoral artery, an atherosclerotic intimal lesion with an average cross-sectional area of 0.452 mm2 was present in 98% of the animals. The lesion was typically eccentric in location and contained both superficial- and deep-intimal lipid-filled monocyte-macrophages, extracellular lipid, smooth muscle cells, and extracellular connective tissue matrix. The relative percent lipid composition of the iliac-femoral lesion was 62% cholesteryl ester, 21% free cholesterol, and 17% phospholipid. Thus, we conclude that the combination of meal feeding a cholesterol/fat diet, dietary regimen and chronic mild endothelial injury in the rabbit results in (1) a diet-induced hypercholesterolemia in which LDL appear to be the predominant lipoprotein; and (2) a lesion within the iliac-femoral artery comparable in histologic and chemical composition to a human fatty streak.

Rapid on-line determination of cholesterol distribution among plasma lipoproteins after high-performance gel filtration chromatography

A high-performance gel chromatography (HPGC) system has been developed which allows the unattended on-line determination of lipoprotein cholesterol distribution (VLDL-C, LDL-C, HDL-C), within 40 min, in microliter quantities of plasma using a single, relatively inexpensive column (Superose 6HR). The FAST cholesterol reagent (Sclavo) and a knitted PFTE Kratos reaction coil (Applied Biosystems) were found to provide optimal sensitivity, linearity, resolution, and dispersion characteristics. Validation is provided by comparison to target values for human quality control reference sera, and by comparing the values obtained by HPGC to the beta-quant method (LRC). The utility of the system is illustrated by comparing profiles from seven different species with normal or elevated plasma cholesterol concentrations. This technique allows rapid analysis of samples, regardless of species, without the use of precipitating agents or the ultracentrifuge. It could also be applied for the direct clinical determination of LDL-cholesterol.

Extracellular lipid deposition in atherosclerosis

Atherosclerotic lipid deposits found in the core region of fibrous plaques are almost entirely extracellular, but it is not known whether they are derived from necrosis of cells containing accumulated lipid or from direct extracellular lipid accumulation. New evidence pertaining to this question has been obtained through the use of recently developed techniques for preserving and staining lipids in electron microscopy, and through a detailed morphologic and chemical examination of human aortic fibrolipid lesions, which are progenitor lesions for fibrous plaques. The evidence favours a substantial role, perhaps a dominant role, for extracellular lipid accumulation in the formation of the fibrous plaque core region.

Quantitation and localization of apolipoproteins [a] and B in coronary artery bypass vein grafts resected at re-operation

Lp[a] is a lipoprotein whose plasma concentration is highly correlated with cardiovascular disease. Its protein moiety, apoLp[a], consists of two large polypeptides, apo[a] and apo B. The possible contribution of Lp[a] to atherosclerosis in saphenous vein aortocoronary bypass grafts was studied in a population of patients undergoing coronary re-bypass surgery. The vein graft tissue levels of apoLp[a] were compared with graft duration, gross and light microscopic pathology, as well as plasma levels of apoLp[a]. The localization pattern of apo[a] and apo B in vein graft tissue was determined. In addition, the plasma levels of cholesterol, triglycerides, apoproteins (apo) A-I, A-II, and E were measured. In a representative subpopulation of 17 patients with a mean age of 63 years from whom grafts with a mean duration of 112 months were resected, the mean total plasma cholesterol level was 221 mg/dl, the mean high density lipoprotein cholesterol level was 31 mg/dl, and the mean plasma triglyceride level was 228 mg/dl. In normal saphenous veins, the level of apoLp[a] was below measurable limits (less than 2 ng/mg), and the level of apo B was very low (3.3 ng/mg). In resected grafts, the mean tissue level of apoLp[a] was 32 ng/mg, and that of apo B was 70 ng/mg, demonstrating the net accumulation of these apoproteins in veins from the time of their grafting into the arterial bed. The apoLp[a]/apo B ratio was determined in 77 tissue segments from 59 grafts (28 patients) and was found to be 0.313. This tissue ratio was significantly higher (p = 0.02) than the plasma apoLp[a]/apo B ratio from these patients, which was 0.132. Immunostaining showed co-localization of apo[a] and apo B in the neointima of grafts. The most abundant pathologic features observed in resected grafts were proliferated intima (43/52), thrombus (28/52), and atherosclerotic core regions (21/52). The level of tissue apo B correlated well with the abundance of core regions (r = 0.501), whereas the level of tissue apoLp[a] did not correlate as well with this feature (r = 0.233). Although apo[a] and apo B are almost absent from normal saphenous vein, these apoproteins (and presumably the lipoproteins Lp[a] and low density lipoprotein) accumulate in bypass vein grafts. The data support the view that these lipoproteins play a significant role in vein graft atherosclerosis.

Lactosaminated Fab fragments specific for low density lipoproteins/hepatocyte targeting and hypolipoproteinemic activity

We have previously reported that Fab fragments of IgGs modified by lactosamination (lac-Fab) can direct macromolecules, including low density lipoproteins (LDL), to the liver. In the present paper we demonstrate that lac-Fab that is specific for LDL is an effective and selective hypolipoprotein agent. A plasma pool of about 60 mg/dl of apoprotein B (apo B) was induced in rats by bolus injection of human LDL (hLDL), which increased the cholesterol value to about 150 mg/dl. Three hours after injection of the highest dose of lac-Fab, the total cholesterol decreased to 80 mg/dl, compared to 120 mg/dl in control animals. Studies conducted with 131I-tyramine-cellobiose-labeled LDL indicated that the liver was the only organ in which lac-Fab increased LDL uptake and degradation. The effect of lac-Fab was dose-dependent. With amounts of lac-Fab between 13 to 42 mg/kg body weight, the amount of hLDL cleared through the lac-Fab mechanism ranged from 30% to 70% of the initial pool. Analysis of the plasma lipoprotein subfractions revealed that high density lipoprotein levels were not affected. Histologic examination of liver sections after sequential injection of fluorescently labeled hLDL and lac-Fab indicated specific uptake in the hepatocytes when compared to control sections obtained from animals injected with Dil-LDL alone. The uptake of fluorescent LDL induced by lac-Fab was completely prevented by a co-injection of an excess of asialofetuin. We conclude that lac-Fab that is specific for LDL is a selective hypolipoproteinemic agent and a specific carrier to the hepatocytes.

Human aortic fibrolipid lesions. Immunochemical localization of apolipoprotein B and apolipoprotein A

Comparative localization of apolipoproteins (apo) B and A in small, raised fibrolipid lesions was performed to determine whether low density lipoproteins (LDL) and high density lipoproteins (HDL) may be involved in the formation of the earliest identifiable lipid-rich core regions found in atherosclerotic fibrous plaques. Apo B was observed associated with the superficial layer of foam cells in collagenous areas of the lesion cap and within the lipid-rich core region. The lipid-rich core region was well-circumscribed by an intense band of apo B staining along both luminal and medial aspects. Apo A staining was confined to the noncellular elements of the fibrolipid lesion. Collagenous areas were speckled with fine, punctate granules of immunoreactive apo A. A homogeneous, granular apo A staining pattern was characteristic throughout the core region. With these data from a relatively early lesion in the development of the atherosclerotic fibrous plaque, we conclude that: 1) both LDL and HDL can accumulate in the lipid-rich core region since no preferential staining for apo B over apo A was observed in this region, and 2) the paucity of cell-associated apo A staining in small fibrolipid lesions suggests that HDL interacts with the arterial wall differently than does HDL.

Ultrastructure of the human aortic fibrolipid lesion. Formation of the atherosclerotic lipid-rich core

The formation of the atherosclerotic lipid-rich core has been elucidated by electron microscopy of the core region in small, raised fibrolipid lesions. The relationship among lipid deposits, extracellular matrix, and cells found in distinct regions of the fibrolipid lesion was examined. Extracellular lipid droplets, verified by osmium-thiocarbohydrazide-osmium staining, made up approximately 40% of the lipid-rich core volume. The lipid droplets were often found distinctly associated with elastin and/or collagen; these associations were dependent upon the location examined within or near the lipid-rich core. Within areas of intense extracellular lipid deposits, crystalline clefts suggesting cholesterol monohydrate were observed. Stereologic analysis of the lipid-rich core components revealed marked reductions in the volume fractions of cells, reticular ground substance, and basement membrane; while the extent of extracellular lipid increased 7-10-fold. Eleven percent or less of lipid in the core region was found within cells, usually smooth muscle cells. Above the core region in the lesion cap, monocyte-macrophage foam cells were prominent. Cellular lipid droplets were much larger (profile diameters sixfold higher) than extracellular droplets. With these data as well as transitional morphologic features at the boundaries of the core region, it is suggested that the abundant extracellular lipid does not derive from cell necrosis, and lipid deposition in association with extracellular matrix constituents is an early event in the development of the lipid-rich core.

Quantitative ultrastructural analysis of perifibrous lipid and its association with elastin in nonatherosclerotic human aorta

Nonatherosclerotic areas in human arteries display an age-related accumulation of cholesteryl ester in the form of small, perifibrous lipid droplets in the deeper intimal layers. We treated human aortic specimens with an osmium-thiocarbohydrazide-osmium sequence en bloc after glutaraldehyde fixation in order to provide electron dense staining of neutral lipid for ultrastructural study. Neutral lipid was quantified in terms of area fractions on thin sections. Extracellular lipid, primarily in the form of small (less than 300 nm) droplets, accounted for 91% of the lipid found in the deep intimal region. Seventy-four percent of extracellular lipid appeared in droplets or aggregates that were demonstrated as adjacent to or within elastic fibers in the plane of section. The fraction of lipid adjacent to elastin in three dimensions is likely to be considerably higher than 74%. The results support the concept that an interaction between elastin or its associated components and lipids or lipoproteins may be important in extracellular lipid deposition in human arteries.

Human aortic fibrolipid lesions. Progenitor lesions for fibrous plaques, exhibiting early formation of the cholesterol-rich core

The early development of the lipid-rich core and other features of atherosclerotic fibrous plaques has been elucidated by examining discrete, small regions of raised intima in human aorta, which often bear a resemblance to both fatty streaks and fibrous plaques. Approximately one-fourth of small raised lesions (less than 16 sq mm of surface area) contained little or no stainable lipid, while three-fourths had a characteristic appearance, which included a superficial layer of foam cells, a core of noncrystalline and/or crystalline lipid, and a developed or developing collagenous cap. Total intimal volumes of the lipid-containing lesions, termed "fibrolipid lesions," ranged from 3 to 43 microliters, with the majority less than 16 microliters. Core lipid in the smallest lesions was located in the musculoelastic layer of the intima. In larger lesions the core extended luminally into the elastic hyperplastic layer, and cholesterol crystals were found more frequently. Total cholesterol concentration in fibrolipid lesions was similar to that in fatty streaks; however, the ratio of unesterified to total cholesterol was relatively high, similar to that found in fibrous plaques. It is concluded that 1) the formation of a lipid-rich core and cholesterol crystallization are early events in the development of many raised lesions; 2) the consistent association between the superficial layer of foam cells and the deep-lying lipid-rich core raises the possibility of an influence, possibly indirect, of foam-cell lipid metabolism on core formation; and 3) the fibrolipid lesion may represent one stage in a potential transitional morphologic sequence between fatty streak and fibrous plaque.

Interferometric analysis of intrasection and intersection thickness variability associated with cryostat microtomy

Mach-Zehnder interferometric measurements were used to assess the extent of section thickness variability (inter- and intrasection) associated with cryostat microtomy of adrenal sections over a typical working range of 10-20 micron. Sections were obtained using a Bright's Cambridge rocking type and a Damon rotary type cryostat microtome to allow comparative analyses. The effective thickness of tissue sections after being mounted onto slides by flash drying was reduced by 90% relative to microtome section thickness setting. A linear relationship between measured thickness and microtome setting was obtained with both instruments. Thickness variability between replicate sections over the range of microtome settings approximated 11% for the rocking microtome and 5% with the rotary microtome. Average intrasection variability was found to be 7% for rocking microtome sections and 4% for sections obtained with the rotary microtome. However, this variability is a negligible source of error in cytophotometric analyses, providing replicate sections are used and an adequate number of measurements are made on mask-delimited individual cells or tissue specimen areas.

Brain neuronal RNA metabolism during acute soman toxication: effects of antidotal pretreatments

Effects of various antidotal treatments on neuronal RNA contents and on soman induced RNA and acetylcholinesterase (AChE) depletion were monitored using quantitative cytochemical techniques. In rats only with antidotes, atropine depressed whereas pralidoxime (2-PAM) elevated RNA contents of both caudate and cerebrocortical (Layer V) neurons. Soman produced a virtually complete inhibition of AChE activity and a moderate decline in neuronal RNA contents. Atropine pretreatment partially restored neuronal RNA levels. Atropine + 2-PAM prophylaxis eventuated in a complete restoration of RNA levels but no reactivation of AChE. Addition of physostigmine to the atropine + 2-PAM treatment regimen resulted in appreciable AChE reactivation but reduced RNA levels. The overall data indicate that: (1) soman-induced neuronal RNA depletion can be completely reversed by antidotal pretreatments; (2) no precise relationship exists between the extents of antidote-induced restoration of RNA and AChE levels; and (3) 2-PAM exerts marked effects on the brain neuronal network which are unrelated to AChE reactivation. It is postulated that effects of soman and antidotes on neuronal RNA metabolism may signify alterations in acetylcholine (ACh) sensitivity and that pharmacologic manipulation of ACh responsiveness during organophosphate cholinesterase poisoning may be a mechanism for additional therapeutic intervention.

Scanning-integrating cytophotometric analyses of brain neuronal RNA and acetylcholinesterase in acute soman toxicated rats

Cytophotometric analyses of RNA and acetylcholinesterase responses of caudate and cerebrocortical neurons of soman toxicated rats were conducted to characterize impairments in regulatory aspects of neuronal metabolism occurring in the acute phase of cholinesterase impairment. There was a severe and dose-dependent suppression (20-60%) in neuronal acetylcholinesterase activity in both a.m. and p.m.-treated rats; no diurnal differences were apparent in control acetylcholinesterase levels or neuronal acetylcholinesterase responsiveness to soman toxication. RNA levels, however, were markedly higher in p.m. than in a.m. saline-treated controls. Soman depressed caudate neuron RNA contents in the afternoon, but not in the morning. Cerebrocortical neuron RNA levels were suppressed in both a.m. and p.m.-toxicated rats, although this RNA depletion was more severe in the afternoon. These results indicate that soman can elicit marked alterations in neuronal transcriptional-translational capabilities and that there are diurnal variations in cellular metabolic responsiveness to soman toxication. Although functional relationships between soman-induced cholinesterase inhibition and RNA depletion remain to be elucidated, depressed RNA metabolism appears to be a maladaptive response preventing rapid regeneration of cholinesterase following poisoning.